It is known to cool electrical machinery, for example A.C. generators in motor vehicles, by use of fans or other ventilators, preferably attached directly to the rotor shaft of the generator. The fans may be mounted within the housing of the generator or externally thereof and serve to generate a substantially axial air flow through the electrical machinery. Cooling a generator or other electrical machinery by means of an axially air transporting fan has several disadvantages. The power required to drive the fan increases non-linearly with increasing speed and this power drain is present even if no cooling is required; the air transported by the fan generally carries contaminants, dust and the like, which may accumulate within the generator and tend to diminish the cooling efficiency; the rotating fan generates substantial noise and may also serve as a diaphragm for transmitting noise generated by axial oscillations of the generator shaft.
The rotating cooling fan in the known apparatus must be so dimensioned that is can supply adequate cooling even when the outside air temperature is extremely high and the A.C. generator is subjected to its heaviest load. Accordingly, either the fan power, or the generator must be adequate for these maximum conditions. The interior of the generator must contain air guide channels that pass in the vicinity of those parts of the generator that produce the most heat. All of these efforts increase the cost and decrease the efficiency of which the A.C. generator is inherently capable. Encapsulated generators present even more difficult cooling problems.
It is known in many areas of technology to transport heat also for the purpose of cooling, by the use of heat pipes which are inherently capable of transporting substantial amounts of heat from one location to another. A heat pipe of known construction has a partial region extending into a cool zone; its interior contains a heat carrier, for example an evaporable transport medium or coolant which is heated in the region where heat is generated to a degree that it will evaporate. Its vapor will migrate within the heat pipe to the cooler region. In the cooler region, the coolant condenses, after which it is transported back into the evaporation region due to the capillary forces. The maximum heat transport capability of such heat pipes is determined by the strength of the capillary forces and by the pressure drops of the vapor flow and the liquid flow.
It is known to use heat pipes for cooling thyristors, for example as described in Brown Boveri Company (BBC) News, 1973, Vol. 6/7, Page 143ff.